Radiation sensitive compositions and methods

ABSTRACT

The present invention provides radiation sensitive compositions and methods that comprise novel means for providing relief images of enhanced resolution. In one aspect the invention provides a method for controlling diffusion of photogenerated acid comprising adding a polar compound to a radiation sensitive composition and applying a layer of the composition to a substrate; exposing the composition layer to activating radiation whereby a latent image is generated comprising a distribution of acid moieties complexed with the polar compound; and treating the exposed composition layer to provide an activating amount of acid.

This application is a continuation of application Ser. No. 09/372,635filed on Aug. 11, 1999 now U.S. Pat. No. 6,607,870, which application isa continuation application of application Ser. No. 08/152,084 nowgranted as U.S. Pat. No. 5,968,712, which application is a file wrappercontinuation of application Ser. No. 07/778,729, filed Oct. 17, 1991 nowabandoned.

BACKGROUND OF THE INVENTION

1. Introduction

The invention relates to radiation sensitive compositions such asphotoresists that provide relief images of enhanced resolution. Moreparticularly, the invention relates to compositions and methods thatcomprise novel means for treating photoacid-generating compositions toprovide relief images of enhanced resolution and to control diffusion ofphotogenerated acid.

2. Background Art

Photoresists are used to form photosensitive films used for transfer ofan image to a substrate. After a coating of a photoresist is formed on asubstrate, the coating is selectively exposed through a photomask to asource of activating radiation. The photomask has areas that are opaqueto activating radiation and other areas that are transparent toactivating radiation. Exposure to activating radiation provides aphotoinduced chemical transformation of the photoresist coating tothereby transfer the pattern of the photomask to the resist coatedsubstrate. Following exposure, the photoresist is developed to provide arelief image that permits selective processing of the substrate.

A photoresist can be either positive-acting or negative-acting. For mostnegative photoresists, those coating layer portions that are exposed toactivating radiation polymerize or crosslink in a reaction between aphotoactive compound and polymerizable reagents of the resistcomposition. Consequently, the exposed coating portions are renderedless soluble in a developer solution than unexposed portions. For apositive-acting photoresist, exposed portions are rendered more solublein a developer solution while areas not exposed remain comparativelyless developer soluble.

Following development of a photoresist coating, portions of thesubstrate bared by development may be altered such as by chemicaletching or plating. The historical background, types and processing ofconventional photoresists are described by DeForest, PhotoresistMaterials and Processes, McGraw Hill Book Company, New York, ch. 2,1975, and by Moreau, Semiconductor Lithography, Principles, Practicesand Materials, Plenum Press, New York, ch. 2 and 4, 1988, bothincorporated herein for their teaching of photoresist compositions andmethods of making and using the same.

Most commercial photoresist formulations, both positive and negative,comprise a film forming resin binder and a radiation sensitivecomponent. Many of the film forming binders in use are phenolic resins.For example, most positive acting photoresists currently in commercialuse comprise a novolak resin and a naphthoquinone diazide sulfonic acidester photoactive compound where the novolak resin is the reactionproduct of formaldehyde and a phenol. Examples of such photoresists aredisclosed in U.S. Pat. Nos. 4,377,631 and 4,404,272, both incorporatedherein by reference. Another class of positive acting photoresistscomprise a poly(vinylphenol) and a naphthoquinone diazide acid ester.Examples of these photoresists are disclosed in U.S. Pat. Nos. 3,869,292and 4,439,516, both incorporated herein by reference.

Many negative acting photoresists also utilize phenolic resins as thefilm-forming component of the resist. For example, photoresistcompositions of particular utility in high resolution deep-UVlithography have been developed based on the use of a photoacidgenerator sensitive to selective wavelengths of radiation, acrosslinking agent, and a phenolic, acid-hardening, polymeric binder. Inthese systems, radiation is used to cleave the photoacid generator, thuscreating a strongly acidic environment. Upon subsequent heating (aprocessing step referred to as the “post exposure bake”), the generatedacid activates the crosslinking agent to react with the phenolic binderand thereby form a base insoluble negative image (negative-tone resist).The acid acts as a catalyst for the crosslinking, i.e., there are manycrosslinking events per unit of acid generated in the film. Resists thatrely on acid catalysts, such as these acid-hardening resists, have beenclassified generally as “chemically amplified photoresists”.

In addition to catalyzed crosslinking, other chemically amplifiedmechanisms are known, for example, catalyzed deprotection. Exemplary ofsuch a system is a positive-tone resist comprising a phenolic resin, aradiation sensitive component which generates acid upon irradiation, anda dissolution inhibitor which is not photosensitive itself, but ischemically decomposed in an acid-catalyzed deprotection reaction. Aswith the above described negative-acting system, the acid catalyst iscatalytic, inducing a series of deprotection reactions upon heatingduring the post exposure bake.

More specifically, a deprotection process can be represented by thefollowing equations:

Acid Generation Reaction

AG+hv--->AH+G--->A⁻+H⁺+G

Deprotection Reaction

H⁺+Poly-o-p--->Poly-OH+H⁺

In the above reactions, the acid-generator (AG) molecule is converted toa strong acid (AH) upon absorption of a photon (hv), i.e., upon exposureto activating radiation. The acid proton affects the desireddeprotection reaction of the protected polymer (Poly-o-p, where Poly-Ois a hydroxyl-substituted polymer and p is a protecting group) toprovide the deprotected polymer (Poly-OH) at a rate which is a functionof the acid concentration [H⁺], temperature, diffusion rate of the acidin the polymer matrix and the process environment. A crosslinkingmechanism operates similarly, the acid proton affecting the reactionbetween the crosslinker and the reactive polymer of the composition.

Adequate resolution of a patterned image generally requires that theradiation generated acid concentration, [H⁺], remain substantiallyconstant within the exposed regions of a layer of the composition. Theexposure process defines the latent image by transferring information tothe resist coating layer by means of the phototool and the exposureradiation. This information is stored in the resist as photogeneratedacid. Any loss of this information (i.e., acid) into unexposed regionsof the resist, or into the substrate or environment can reduce theresolution of the transferred image.

In chemically amplified resists, it is generally important to havesufficient diffusion of photogenerated acid so that enough catalyticconversions occur to provide required photospeed. On the other hand andas discussed above, it is also important to limit diffusion ofphotogenerated acid to avoid information loss from exposed regions of acoating layer. Striking a satisfactory balance between these twoobjectives, however, can be difficult. Photogenerated acid often tendsto diffuse into unexposed regions of a photoresist coating layer, orinto the environment or the substrate. Upon subsequent heating duringthe post exposure bake, the acid-catalyzed reaction will occur in thoseunexposed regions where the acid has diffused, compromising resolutionof the patterned image.

Methods for controlling diffusion of acid through an exposed photoresistlayer have included redesign of the polymer matrix to provide largemolecules to slow movement of the photogenerated proton, or toincorporate large molecules of photoacid compounds which generate largeacid molecules. The use of large molecules has the disadvantage ofdecreasing the number of catalytic cycles for the chemically amplifiedprocess, thus decreasing the sensitivity of the resist.

Another method to control acid diffusion has been to limit the periodbetween exposure and the post exposure bake. This can require design ofrelatively sophisticated and more costly interchanges between thephototool and baking apparatus.

SUMMARY OF THE INVENTION

The present invention provides radiation sensitive compositions andmethods for treating such compositions, including methods for enhancingresolution of the relief image of a radiation sensitive composition andmethods for controlling diffusion of photogenerated acid. Thecompositions of the invention may include various types of resin matrixsystems and acid generators and comprise a means of effectivelycontrolling loss of contrast due to the effects of acid diffusion duringpost exposure residence times. The compositions preferably comprisephenol-based resin systems. As used herein, the term “acid generator”refers to a compound capable of generating acid upon exposure toactivating radiation.

The invention is based on the discovery that addition of certain polarcompounds to a photoacid-generating composition provides enhancedresolution of images patterned in said compositions. It is believed theaddition of such polar compounds results in the formation of a complexof the polar compound and photogenerated acid. By selecting anappropriate polar compound, an activating amount of acid is liberatedfrom the complex during the post exposure bake to effect the desiredacid-catalyzed reaction (e.g., deprotection or crosslinking). Bycomplexing the photogenerated acid with the polar compound, diffusion ofthat acid out of exposed regions is prevented or at least significantlyinhibited. Consequently the invention enhances resolution of a patternedimage relative to prior systems, particularly when processing conditionsimpose delay between imaging and the post exposure bake.

Thus in one aspect the invention provides a method for treating aphotoacid-generating composition comprising adding a suitable polarcompound to the composition. In another aspect the invention providesthe method of adding a polar compound to a radiation sensitivecomposition such as a photoresist and applying a layer of thecomposition to a substrate; exposing the composition layer to activatingradiation whereby a latent image comprising acid moieties complexed withthe polar compound is generated; and treating the exposed compositionlayer to provide an activating amount of acid from the complex. Theexposed composition is preferably treated by heating the layer to atemperature sufficient to provide an activating amount of acid.

The polar compound has one or more moieties that can serve as a base andcomplex with the photogenerated acid at room temperature. Amines arepreferred moieties. The polar compound should be compatible with theresist and resist processing conditions. For example, an effectiveamount of the polar compound preferably should remain in the radiationsensitive composition after any pre-exposure soft bake. Further, thepolar compound should have an appropriate PK_(a) 50 that an activatingamount of acid is released from the formed complex during the postexposure bake. If the polar compound has a pK_(a) value that is toohigh, sufficient acid may not be liberated from the acid-polar compoundcomplex at post exposure bake temperatures and thereby inhibit orprevent the desired acid-catalyzed reaction. As discussed infra,effective amounts of the polar compound can vary with the basicity ofthe polar compound.

Novel articles of manufacture also are provided consisting of substratescoated the compositions of the invention.

The term “activating amount of acid” as used herein means an amount ofacid sufficient to catalyze a desired reaction (e.g., deprotection orcrosslinking) substantially throughout an exposed region of a coatinglayer of a photoacid-generating composition, and to thereby provide asolubility differential sufficient between exposed and unexposed regionsof the coating layer to yield a relief image upon development.

The terms “crosslink” and “crosslinking” as used herein refer to anyreaction of the crosslinking agent(s) of the compositions of theinvention that results in reduced developer solubility. For example, theterms refer to, but are not limited to, any reaction that reduces thenumber of free phenolic hydroxyl sites of a phenol-based polymer, suchas the reaction of a crosslinker agent with multiple hydroxyl sites aswell as reaction of a crosslinker agent with a single hydroxyl site.

DETAILED DESCRIPTION OF THE INVENTION

The polar compounds useful in the invention are characterized by havingone or more moieties that can complex with photogenerated acid. Acomplex of the polar compound and acid should release an activatingamount of acid upon heating at temperatures of the post exposure bake toeffect the desired acid-catalyzed reaction. Typically post exposure baketemperatures range from about 50° C. or greater. Hence a complex ofphotogenerated acid and the polar compound suitably releases anactivating amount of acid at about 50° C. or greater. Post exposurebakes of 80° C., 100° C., 110° C., 120° C., 140° C. or greater arecommon; therefore release of an activating amount of acid at any ofthese temperatures or greater can be suitable.

It is common to perform a pre-exposure bake after coating a liquidphotosensitive composition on a surface to remove solvents. Such apre-exposure bake is typically conducted at temperatures of 90° C. orless. It is thus preferred that a sufficient amount of the polarcompound remain disposed within a radiation sensitive composition, andnot be volatilized, at such pre-exposure bake temperatures, so that aneffective amount of the polar compound is present to complex with acidgenerated during imaging.

The polar compounds of the invention comprise one or more polarfunctional groups so that the compound is sufficiently basic to complexwith photogenerated acid. Suitable polar functional groups include, forexample, ether, ester, amide (including N-substituted amides andN-unsubstituted amides such as acetamide and urea) and amines. Amineshave been found to be preferred polar moieties.

For the photogenerated acid-polar compound complex to release anactivating amount of acid during post exposure bake temperatures, thepK_(a) of the polar compound must be sufficiently low. As used herein,the term “pK_(a)” is used in accordance with its art recognized meaning,that is, pK_(a) is the negative log (to the base 10) of the dissociationconstant of the polar compound in aqueous solution at about roomtemperature.

Effective results can be achieved if the pK_(a) of the polar compound isabout 8.0 or less, although polar compounds having a pK_(a) of greaterthan about 8.0 can be suitable (e.g., a pK_(a) of about 9.0 or less)provided a sufficiently high temperature post-exposure bake is employedto release an activating amount of acid from the polarcompound-photogenerated acid complex. Preferably, a polar compound isused that provides a pK_(a) of about 7.0 or less, more preferably apK_(a) of about 4.0 or less, still more preferably a pK_(a) of about 3.2or less. It should be appreciated, however, that the environments inwhich the polar compounds of the invention are typically used, namelyorganic-based photoacid-generating compositions, are different than theaqueous solutions in which the above pK_(a) values are determined.Hence, polar compounds having pK_(a) values somewhat outside the abovedescribed preferred ranges also may be suitable for purposes of theinvention.

It also should be appreciated that the weaker the basicity of the polarcompound, relatively larger amounts of the polar compound may need to beadded to a photoacid-generating composition to form a complex of thephotogenerated acid and the polar compound. Conversely, the stronger thebasicity of the polar compound, a relatively lower concentration of thepolar compound will be required to form a complex of the photogeneratedacid and the polar complex, and relatively lesser amounts of the polarcompound can be added to a photoacid-generating composition to realizeeffective results, for example enhanced resolution of a patterned imageof the composition.

As indicated above, amines are preferred polar compounds. Suitableamines will include, for example, aryl substituted amines includingphenyl substituted amines such as 4-(p-aminobenzoyl) aniline, 4-benzylaniline, 2-bromo aniline, o-chloro aniline, m-chloro aniline,3,5-dibromo aniline, 2,4-dichloro aniline, N,N-dimethyl-3-nitro aniline,2-fluoro aniline, 2-iodo aniline, 3-nitro aniline, 4-nitro aniline,2-amino benzoic acid, 4-aminoazo benzene, 4-dimethylaminoazo benzene,n-diphenylamine, and phenyl glycine; cyclic amines (includingnitrogen-containing aromatics) such a nicotine, 3-acetyl piperidine,proline, hydroxy proline, 2-amino-4-hydroxy pteridine, purine, 8-hydroxypurine, pyrazine, 2-methyl pyrazine, methylamino pyrazine, pyridazine,2-amino pyrimidine, 2-amino-5-nitro pyrimidine, 3-bromo pyridine,3-chloro pyridine, 2-hydroxy pyridine, 4-hydroxy pyridine, quinazoline,8-carboxy quinoline, quinoaline, thiazole, and tryptophan; and aliphaticamines and substituted aliphatic amines (including carboxy-substitutedaliphatic amines) such as arginine, aspartic acid, betaine,glycyl-2-amino-n-butyric acid, cystine, 1-glutamic acid, glycine, glycylglycine, glycylglycyl glycine, leucyl glycine, methyl glycine, n-propylglycine, tetraglycyl glycine, hexamethylene diamine, histidine,carnosine, 2-amino isobutyric acid, isoleucine, leucine, glycyl leucine,norleucine, ornithine, serine, threonine, methionine, glycylalanine,methoxy alanine, and threonine.

Relatively strong bases can form too strong a complex withphotogenerated acid and, consequently, use of such bases can preventrelease of an activating amount of acid at typical post exposure baketemperatures. Therefore less suitable polar compounds for purposes ofthe present invention are relatively strong bases that upon complexingwith a photogenerated acid will not provide an activating amount of acidat typical post exposure bake temperatures. For example, bases having apK_(a) of about 9.0 or greater are less suitable for purposes of thesubject invention, and thus are excluded from the preferred embodimentsof the invention. Polar compounds having a pK_(a) of about 10.0 orgreater, or 11.0 or greater will be even less suitable; such strongbases will have limited utility in the processes of the invention, andthus are also excluded from the preferred embodiments of the invention.Such less suitable and strongly basic compounds include, for example,trialkylamines such as triethylamine; monoalkylamines such asethylamine,propylamine, butylamine, heptylamine, hexylamine, octylamine, andnonylamine; and other strong bases such as trimethylimidine,2-aminoethyl benzene, dimethyl glycine, and triamino propane.

The polar compounds of the invention may be used in both positive-actingand negative-acting radiation sensitive compositions, includingpositive-acting and negative-acting photoresists. Positive tonecompositions are generally based on a two component system comprising aresin binder and an acid generator compound. A preferred resin binder isa phenol-based polymer. Negative tone compositions are typically threecomponent systems comprising a resin binder, an acid generator compoundand a crosslinking agent. As discussed, for a negative resist, thephotogenerated acid catalyzes a reaction between the crosslinker and areactive hydrogen containing material such as a phenol-based resin.

Phenol-based polymers useful for these acid-generating compositions areknown in the art and typically comprise novolak and poly(vinylphenol)resins and copolymers of the same with styrene and alpha-methylstyrene.Novolak resins are thermoplastic condensation products of a phenol, anaphthol or a substituted phenol, such as, cresol, xylenol, ethylphenol,butylphenol, isopropyl methoxyphenol, chlorophenol, bromophenol,resorinol, naphthol, chloronaphthol, bromonaphthol or hydroquinone withformaldehyde, acetaldehyde, benzaldehyde, furfural acrolein, or thelike. Suitable novolak resins are disclosed in U.S. Pat. Nos. 3,148,983;4,404,357; 4,115,128; 4,377,631; 4,423,138; and 4,424,315, thedisclosures of which are incorporated herein by reference.

Poly(vinylphenol) resins are thermoplastic polymers that may be formedby block polymerization, emulsion polymerization or solutionpolymerization of the corresponding monomers in the presence of acationic catalyst. Vinylphenols useful for the production ofpoly(vinylphenol) resins may be prepared, for example, by hydrolysis ofcommercially available coumarin or substituted coumarins, followed bydecarboxylation of the resulting hydroxy cinnamic acids. Usefulvinylphenols may also be prepared by dehydration of the correspondinghydroxy alkyl phenols or by decarboxylation of hydroxy cinnamic acidsresulting from the reaction of substituted or non-substitutedhydroxybenzaldehydes with malonic acid. Preferred poly(vinylphenol)resins prepared from such vinylphenols have a molecular weight range offrom about 2,000 to about 100,000 daltons.

Another preferred phenol-based resin for the radiation sensitivecompositions of the invention are copolymers of phenols and nonaromaticcyclic alcohols analogous in structure to the novolak resins and thepoly(vinylphenol) resins. Such copolymers provide a radiation sensitivecomposition with relatively greater transparency to activatingradiation. These copolymers may be formed in several ways. For example,in the conventional preparation of a poly(vinylphenol) resin, a cyclicalcohol may be added to the reaction mixture during the polymerizationreaction which is thereafter carried out in normal manner. The cyclicalcohol is preferably aliphatic, but may contain one or two doublebonds. The cyclic alcohol is preferably one closest in structure tophenol. For example, if the resin is poly(vinylphenol), the comonomerwould be vinyl cyclohexanol.

The preferred method for formation of the copolymer compriseshydrogenation of a preformed novolak resin or a preformedpoly(vinylphenol) resin. Hydrogenation may be carried out using artrecognized hydrogenation procedures, for example, by passing a solutionof the phenolic resin over a reducing catalyst such as a platinum orpalladium coated carbon substrate or preferably over Raney nickel atelevated temperature and pressure. The specific conditions are dependentupon the polymer to be hydrogenated. More particularly, the polymer isdissolved in a suitable solvent such as ethyl alcohol or acetic acid,and then the solution is contacted with a finely divided Raney nickelcatalyst and allowed to react at a temperature of from about 100 to 300°C. at a pressure of from about 50 to 300 atmospheres or more. The finelydivided nickel catalyst may be a nickel-on-silica, nickel-on-alumina, ornickel-on-carbon catalyst depending upon the resin to be hydrogenated.Hydrogenation is believed to reduce the double bonds in some of thephenolic units resulting in a random copolymer of phenolic and cyclicalcohol units randomly interspersed in the polymer in percentagesdependent upon the reaction conditions used.

The mole percentage of cyclic alcohol units of the polymer should notexceed a level where development of the radiation sensitive compositionis prevented following exposure of the composition to activatingradiation. Thus, preferably the polymer has a major proportion ofphenolic units and a minor proportion of cyclic alcohol units, morepreferably the cyclic alcohol units vary from about 1 to 30 mole percentof the polymer binder, and still more preferably from about 5 to 15 molepercent of the polymer.

Other resins suitable for the practice of the invention include polymersmade from polystyrene maleimides with pendant acid labilefunctionalities. Examples of useful polymers include those disclosed inU.S. Pat. Nos. 4,931,379, and 4,939,070, both incorporated herein byreference. Vinylic polymers containing recurrent pendant group are alsouseful and are disclosed in U.S. Pat. No. 4,491,628, incorporated hereinby reference.

Another suitable resin is polyglutarimides, prepared according to U.S.Pat. No. 4,246,374, incorporated herein by reference, having a weightaverage molecular weight ranging from about 1000 to about 100,000 andwhich are soluble in aqueous base and contain at least 40 weight percentof the nitrogen atoms of the NH or ammonia form.

Another suitable resin binder for use in accordance with the inventionare phenol-based polymers that are partially silylated. A preferredsilylated polymer is disclosed in U.S. Pat. No. 4,791,171, incorporatedherein by reference. This patent discloses partially silylatedpoly(vinylphenol) polymers prepared by derivatizing the phenolichydroxide moieties of a poly(vinylphenol) with suitable organosiliconcompounds. Such derivatization can be accomplished, for example, bycondensation of a poly(vinylphenol) with an organosilicon compound thathas a suitable leaving group, for example trimethyl-silylmethylchloride,bromide, mesylate or tosylate; trimethylsilylchloride, bromide, cyanideor mesylate; phenyldimethylsilylchloride; ort-butyldimethylsilylchloride.

For the positive tone radiation sensitive compositions, preferred acidgenerators are naphthoquinone diazide sulfonic acid esters such as thosedisclosed by Kosar, Light Sensitive Systems, John Wiley & Sons, 1965,pp. 343 to 352, incorporated herein by reference. This group of acidgenerators form an acid in response to radiation of differentwavelengths ranging from visible to X-ray. Thus, the generator compoundchosen will depend, in part, upon the wavelengths used for exposure. Byselecting the appropriate acid generator, the radiation sensitivecompositions can be imaged by deep UV, E-beam, laser or any otheractivating radiation conventionally used for imaging photoresists.Specifically preferred acid generators include the2,1,4-diazonaphthoquinone sulfonic acid esters and the2,1,5-diazonaphthoquinone sulfonic acid esters.

Onium salts are also suitable acid generators for use in thecompositions of the invention. Onium salts, with weakly nucleophilicanions are particularly suitable. Examples of such anions are thehalogen complex anions of divalent to heptavalent metals or non-metals,for example, Sb, Sn, Fe, Bi, Al, Ga, In, Ti, Zr, Sc, D, Cr, Hf, and Cuas well as B, P, and As. Examples of suitable onium salts arediaryldiazonium salts and onium salts of group Va and B, Ia and B and Iof the Periodic Table, for example, halonium salts, quaternary ammonium,phosphonium and arsonium salts, aromatic sulfonium salts and sulfoxoniumsalts or seleonium salts. Examples of suitable preferred onium salts canbe found in U.S. Pat. Nos. 4,442,197; 4,603,101; and 4,624,912, allincorporated herein by reference.

A particularly suitable group of acid generating compounds useful in thecompositions of the invention are the iodonium salts. A preferred groupof such salts are those resulting from the condensation ofaryliodosotosylates and aryl ketones as disclosed, for example, in U.S.Pat. No. 4,683,317, incorporated herein by reference.

Other useful acid generators include the family of nitrobenzyl esters,and the s-triazine derivatives. Suitable s-triazine acid generators aredisclosed, for example, in U.S. Pat. No. 4,189,323, incorporated hereinby reference.

Dissolution inhibitors compounds also may be added to the radiationsensitive compositions of the invention to further control dissolutionof an exposed coating layer of the composition. Suitable dissolutioninhibiting compounds include, for example,t-butyloxycarbonato-bis-phenol-A and t-butylacetoxy-bis-phenol-A. Thedissolution inhibiting compounds may be suitably used in a concentrationof about 5 to 10 weight percent of total solids of a radiation sensitivecomposition.

As noted above, negative acid-hardening resist systems generallycomprise three components where photogenerated acid catalyzes a reactionbetween a crosslinker and a reactive hydrogen containing material suchas a phenol-based resin. All of the above described resins are suitableas the reactive hydrogen containing material for the negative-actingcompositions of the invention. Preferred are the above described novolakand poly(vinylphenol) resins. A particularly preferred resin fornegative tone compositions is the above described phenol-based polymerthat contains both phenolic and cyclic alcohol units.

In the negative resist systems, amine-based crosslinkers are preferred.Suitable amine-containing crosslinkers include urea-formaldehyde,melamine-formaldehyde, benzoguanamine-formaldehyde,glycoluril-formaldehyde resins and combinations thereof. Other suitableamine-based crosslinkers include the melamines manufactured by AmericanCyanamid Company such as Cymel^(R) 300, 301, 303, 350, 370, 380, 1116and 1130; benzoguanamine resins such as Cymel^(R) 1123 and 1125;glycoluril resins Cymel^(R) 1170, 1171, 1172; and urea-based resinsBeetle^(R) 60, 65 and 80. A large number of similar amine-basedcompounds are presently commercially available from various suppliers.As known to those in the art, polymeric amine-based resins may beprepared by the reaction of acrylamide or methacrylamide copolymers withformaldehyde in an alcohol-containing solution, or alternatively by thecopolymerization of N-alkoxymethyl acrylamide or methacrylamide withother suitable monomers.

Of the above crosslinkers, the melamines are preferred, and particularlypreferred are hexaalkoxymethylmelamines such as the above identifiedCymel resins.

The amine-based crosslinker and phenol-based polymer are used incombination with an acid generator. Non-ionic, organic acid generatorsare particularly suitable for the negative-acting compositions of theinvention. Particularly preferred non-ionic organic acid generators arehalogenated non-ionic compounds such as, for example,1,1-bis[p-chlorophenyl]-2,2,2-trichloroethane (DDT);1,1-bis[p-methoxyphenyl]-2,2,2-trichloroethane (methoxychlor^(R));1,2,5,6,9,10-hexabromocyclododecane; 1,10-dibromodecane;1,1-bis[p-chlorophenyl]2,2-dichloroethane;4,4′-dichloro-2-(trichloromethyl)benzhydrol or1,1-bis(chlorophenyl)2-2,2-trichloroethanol (Kelthane^(R));hexachlorodimethylsulfone; 2-chloro-6-(trichloromethyl)pyridine;O,O-diethyl-O-(3,5,6-trichloro-2-pyridyl)phosphorothioate (Dursban^(R));1,2,3,4,5,6-hexachlorocyclohexane;N(1,1-bis[p-chlorophenyl]-2,2,2-trichloroethylacetamide;tris[2,3-dibromopropyl]isocyanurate;2,2-bis[p-chlorophenyl]-1,1-dichloroethylene; and their isomers,analogs, homologs and residual compounds. Suitable photoacid generatorsare also disclosed in European Patent Application Nos. 0164248 and0232972, both incorporated herein by reference.

Residual compounds are intended to include closely related impurities orother modifications of the above halogenated organic compounds whichresult during their synthesis and which may be present in minor amountsin commercial products containing a major amount of the above compounds.

Acid generators that are particularly preferred for deep UV exposure(i.e., about 100 to 300 nm) include1,1-bis(p-chlorophenyl)-2,2,2-trichloroethane (DDT);1,1-bis(p-methoxyphenol)-2,2,2-trichloroethane;1,1-bis(chlorophenyl)-2,2,2-trichloroethanol;tris(1,2,3-methanesulfonyl)benzene; and tris(trichloromethyl) triazine.

For negative-tone resist systems, the amine-based crosslinking agent maybe used as the basic substance to enhance resolution of a relief imageof the resist. Again, the basicity of the crosslinking agent should besuch that the base holds the generated photoacid at room temperature andthen releases an activating amount of acid at the elevated temperaturesof the post-exposure bake. Suitable crosslinkers that will release atleast some photogenerated acids at post exposure bake temperaturesinclude the melamine-formaldehyde resins such as highly methylatedmelamine-formaldehyde, partially methylated melamine-formaldehyde, andmixed ether and butylated melamine resins. Of thesemelamine-formaldehyde resins, Cymel 303 (as commercially available fromAmerican Cyanamid Co.) is specifically preferred.

It has been found that photoacid-generating compositions can providewell resolved relief images, even with extended time delays between theexposure and post exposure bake processing steps, where the compositionscomprise crosslinking agents of hexamethoxymethylmelamine (sometimesreferred to herein as “HMMM”), hydrolyzed derivatives of HMMM whichcontain free amine moieties, and condensation products of HMMM includingdimers and trimers of HMMM. Such HMMM derivatives have been described inJ. H. Dijk, et al., Proc. XVtL FATIPEC Congr., II, 326 (1980),incorporated herein by reference. It has also been found that when apure sample of HMMM is used as the sole crosslinking agent (i.e., in theabsence of any hydrolyzed HMMM derivatives or HMMM condensationproducts) in a photoacid-generating composition, a relief image isprovided having inferior resolution relative to the resolution of arelief image formed from a generally comparable composition thatcomprises HMMM, hydrolyzed HMMM derivatives, and HMMM condensationproducts. This is believed to indicate that an unhydrolyzed monomer ofHMMM does not complex with photogenerated acid and thus does not limitdiffusion of photogenerated acid. In turn, it is believed this resultindicates that hydrolyzed HMMM derivatives and/or HMMM condensationproducts such as dimers and trimers of HMMM effectively complex withphotogenerated acid, and that an activating amount of acid is liberatedfrom said complex at post exposure bake temperatures. Hence a preferrednegative acting radiation sensitive composition in accordance with theinvention comprises HMMM, HMMM condensation products, and hydrolyzedderivatives of HMMM that contain one or more amine groups that caneffectively complex with photogenerated acid. It is noted that Cymel 303as obtained from the American Cyanamid Co. comprises HMMM as well asboth hydrolyzed derivatives of HMMM which contain one or more aminegroups and HMMM condensation products such as dimers and trimers ofHMMM.

To enhance resolution of a patterned resist image, a polar compound ofthe above described type may also be used in combination with acrosslinking agent such as a melamine-formaldehyde resin. The term“complexing polar compound”, or in the specific case of an amine a“complexing amine”, is defined to mean herein a polar compound of theinvention as described above, used in combination with and in additionto any conventional components of a radiation sensitive composition. Forexample, in a positive-acting composition, a complexing polar compoundwill be a component of the composition other than the resin binder, acidgenerator and any other conventional additives such as conventional dyesand conventional sensitizers for expanding the composition's spectralresponse. In a negative-acting composition a complexing polar compoundwill be a component of the composition other than a melamine resin orother primary crosslinker, resin binder, acid generator, conventionalsensitizers, conventional dyes or other conventional components of thecomposition. Amines are preferred complexing polar compounds for use incombination with the primary crosslinking agent in a negativephotoresist, and particularly preferred is a negative photoresist thatcomprises a complexing polar compound of an imidazole in combinationwith a primary crosslinker of a melamine resin.

Negative photoresists that employ a melamine crosslinker andphenol-based resin binder often provide somewhat limited resolution withmany acid generators that produce hydrogen halides (e.g., HBr) uponphotoactivation. Exemplary hydrogen halide generators includetris[2,3-dibromopropyl]isocyanurate. Such resolution problems arebelieved to result at least in part from diffusion of the photogeneratedhydrogen halide into unexposed regions during the interval betweenexposure and the post exposure bake crosslinking reaction. Byincorporating a suitable polar compound into such a photoresistcomposition that contains a hydrogen halide-generator compound,resolution improves. Preferred polar compounds for addition to a resistthat contains a hydrogen halide-generator compound include the abovedescribed amines.

The compositions of the invention are generally prepared following priorart procedures for the preparation of photoresists and otherphotocurable compositions. For a liquid coating composition, the solidsportion of the composition is conventionally dissolved in a solvent. Thesolvent used does not constitute a part of the invention. However, forpurposes of exemplification, useful solvents include glycol ethers, suchas ethylene glycol monomethyl ether, ethylene glycol monoethyl ether,ethylene glycol dimethyl ether, methoxy benzene and the like;Cellosolve^(R) esters such as methyl Cellosolve acetate, ethylCellosolve acetate and propylene glycol monomethyl ether acetate;aromatic hydrocarbons such as toluene, xylene and the like; ketones suchas acetone, methyl ethyl ketone, cyclopentanone, cyclohexanone; esterssuch as ethyl acetate, butyl acetate, hexyl acetate, isobutylisobutyrate and butyl lactone; amides such as dimethylacetamide,N-methyl pyrrolidione and dimethyl formamide; chlorinated hydrocarbonssuch as methylene chloride, ethylene dichloride, 1,1,1-trichloroethane,chlorobenzene and ortho-dichlorobenzene; nitrobenzene; dimethylsulfoxide; alcohols such as diacetone alcohol; and mixtures of theforegoing.

Effective results (e.g., enhanced resolution of a relief image) can beachieved if one or more polar compounds of the above described type isadded to a conventional photoresist composition in an amount of fromabout 0.05 to 5.0 weight percent, although it should be clear thateffective amounts may vary with the particular composition and polarcompound(s) that are employed.

The total solids content of the liquid coating compositions of theinvention should not exceed about 60 percent by weight of theformulation and preferably, the solids content varies between about 10and 50 percent by weight of the total composition.

The compositions of the invention are used in a conventional manner andfor conventional purposes. The liquid coating compositions of theinvention are applied to a substrate such as by spinning, dipping,roller coating or other conventional coating technique. When spincoating, the solids content of the coating solution can be adjusted toprovide a desired film thickness based upon the specific spinningequipment utilized, the viscosity of the solution, the speed of thespinner and the amount of time allowed for spinning.

The compositions of the invention are applied to substratesconventionally used in processes involving coating with photoresists.For example, the compositions of the invention may be applied oversilicon or silicon dioxide wafers for the production of microprocessorsand other integrated circuit components. Aluminum-aluminum oxide andsilicon nitride wafers can also be coated with the compositions of theinvention. Another suitable use of the compositions of the invention isas a planarizing layer or for formation of multiple layers in accordancewith art recognized procedures.

For typical photoresist applications, following coating of a compositionof the invention onto a surface, it is subjected to a pre-exposure softbake, i.e. heated to about 90° C. to remove the solvent until preferablythe resist coating is tack free. Thereafter, it is imaged through a maskin conventional manner. The exposure is sufficient to effectivelyactivate the photoactive component of the resist system to produce apatterned image in the resist coating layer and, more specifically, theexposure energy typically ranges from about 10 to 300 mJ/cm², dependentupon the exposure tool. The wavelength of activating radiation will, ofcourse, vary with the photoactive components of a given radiationsensitive composition and will be known to those skilled in the art. Thespectral response of a radiation sensitive composition can be expandedby the use of suitable radiation sensitizer compounds.

Following exposure, the composition is preferably baked at temperaturesranging from about 50° C. to about 140° C. to release an activatingamount of acid from the complex of the polar compound and thephotogenerated acid, and effect the acid-catalyzed reaction. Preferablythe activating amount of acid released from the polarcompound-photogenerated acid complex during post exposure bake issufficient to catalyze a reaction that results in a solubilitydifferential of preferably at least about 10:1, more preferably at leastabout 100:1, between exposed and unexposed regions of a coating layer ofthe radiation sensitive composition. Thereafter, the film is developed,preferably with an aqueous based developer such as an inorganic alkaliexemplified by sodium hydroxide, potassium hydroxide, sodium carbonate,sodium bicarbonate, sodium silicate, sodium metasilicate, aqueousammonia or the like. Alternatively, organic developers can be used suchas choline based solutions; quaternary ammonium hydroxide solutions suchas a tetra-alkyl ammonium hydroxide solution; various amine solutionssuch as ethyl amine, n-propyl amine, diethyl amine, di-n-propyl amine,triethyl amine or methyldiethyl amine; alcohol amines such as diethanolamine or triethanol amine; cyclic amines such as pyrrole, piperidine,etc. In general, development is in accordance with art recognizedprocedures.

Following development, a bake at temperatures of from about 100° C. toabout 250° C. for several minutes may be employed if desired.

The developed substrate may then be selectively processed on thosesubstrates areas bared of the coating composition, for examplechemically etching or plating substrate areas bared of the compositionin accordance with procedures well known in the art. For the manufactureof microelectronic substrates, for example the manufacture of silicondioxide wafers, suitable etchants include a plasma gas etch and ahydrofluoric acid etching solution. The compositions of the inventionare highly resistant to such etchants thereby enabling manufacture ofhighly resolved features, including lines with submicron widths. Aftersuch processing, the composition mask may be removed from the processedsubstrate using known stripping procedures.

The following examples are presented to better illustrate the invention,but are not to be construed as limiting the invention to the specificembodiments disclosed.

Throughout the examples, the partially hydrogenated poly(p-vinylphenol)resins were obtained from Maruzen Oil, Co. of Tokyo, Japan. The degreeof hydrogenation of these poly(p-vinyl phenols) is expressed as % ofaromatic double bonds converted to single bonds, or equivalently as % ofhydroxyphenyl groups converted to hydroxycyclohexyl groups. Alltemperatures throughout this disclosure are in degrees Celsius.

EXAMPLE 1

A photoresist composition was prepared consisting of 10 g ofpoly(p-vinyl)phenol (hereafter “PVP”) at a 10% level of hydrogenation, 2g of t-butyloxycarbonato-bis-phenol-A and 1.5 g oftris(1,2,3-methane-sulfonyl) benzene dissolved in 27.5 g of diethyleneglycol dimethyl ether. This resist formulation was coated to 1.0 micronthickness on three separate silicon wafers (hereafter “the first wafer”,“second wafer” and “third wafer”) using a conventional spin coater. Thewafers were each soft baked at 90° C. for 1 minute, and then exposed for10 seconds on an HTG deep UV exposure unit with a variable opticaldensity mask placed between the source and the wafer. The first waferwas subjected to a time delay between exposure and post exposure bake of5 minutes; the second wafer was subjected to a time delay of 120minutes; and the third wafer was subjected to a time delay of 24 hoursbetween exposure and post exposure bake. All three wafers were postexposure baked at 120° C. for 1 minute. The three wafers were then batchdeveloped in MF-321 (tetramethylammonium hydroxide sold by ShipleyCompany of Newton, Mass.) for 60 seconds. For the first and secondwafers with delay times of 5 and 60 minutes, respectively, the contrastcurves overlapped. For the third wafer stored for 24 hours, it wasobserved that the resist slowed down as a function of the delay betweenexposure and post exposure bake. Further, in the case of the thirdwafer, the photoresist became, for practical purposes, insoluble in thedeveloper. While not wishing to be bound by theory, it is believed thisresult indicates slow diffusion of acid in the unexposed areas leadingto lower concentration of acid in the exposed areas during the bake stepand thereby decreasing the number of blocked sites deprotected in theexposed areas.

EXAMPLE 2

0.1 g of triisopropanol amine was added to 50 g of the photoresistcomposition prepared in Example 1. This photoresist was coated on threeseparate silicon wafers and processed by the same procedures asdescribed in Example 1. The third wafer subjected to a time delay of 24hours between exposure and post exposure bake showed no change in thecontrast curve relative to the first and second wafers subjected to theshorter time delays. It is believed this result indicates that the basecomplexes with the photogenerated acid, confining the acid to exposedareas to provide a sufficient acid concentration to deprotect the t-Bocsites during the post exposure bake.

EXAMPLE 3

A photoresist composition was prepared by mixing 10 g of PVP at 10%hydrogenation, 0.75 g of purified hexamethoxymethylmelamine, and 0.5 gtris(trichloromethyl)triazine dissolved in 28.25 g diethylene glycoldimethyl ether. The resist was coated to 1.0 micron thickness on threeseparate silicon wafers using a conventional spin coater. The waferswere then baked at 90° C. for 1 minute, and then exposed on a GCA ALSLaserstep 5:1 excimer laser stepper. The first wafer was subjected to atime delay between exposure and post exposure bake of 5 minutes; thesecond wafer was subjected to a time delay of 120 minutes; and the thirdwafer was subjected to a time delay of 24 hours. All three wafers werepost exposure baked at 130° C. for 1 minute. The wafers were batchdeveloped in 0.135 N MF-312 (tetramethyl ammonium hydroxide) for 150seconds. As a measure of diffusion, the changes in linewidth of a 0.5micron feature were observed during the time delay between exposure andpost exposure bake. The line width change increased with increasing timedelay between exposure and post exposure bake. For the wafer subjectedto the 24 hour time delay, the 0.5 micron linewidth was reduced to 0.2micron. While again not wishing to be bound by theory, it is believedthis loss of linewidth resulted from diffusion of acid into theunexposed regions of the resist coating layer, leading to less acid inthe exposed areas and hence linewidth shrinkage as if the resist layerhad been underexposed.

EXAMPLE 4

A photoresist composition was prepared by adding 0.1 g of2-methylimidazole to 50 g of the photoresist composition prepared inExample 3. This imidazole photoresist composition was coated on threeseparate silicon wafers and processed by procedures the same as thosedescribed in Example 3 with time delays between exposure and postexposure bake of 5 minutes, 120 minutes and 24 hours for the first,second and third wafers, respectively. Upon development, no linewidthloss for any of the three wafers was observed. This result is believedto demonstrate that the imidazole base complexes with the photogeneratedacid at room temperature, confining the acid to exposed regions of theresist layer.

The foregoing description of the invention is merely illustrativethereof, and it is understood that variations and modifications can beeffected without departing from the scope or spirit of the invention asset forth in the following claims.

What is claimed is:
 1. A method for forming a photoresist image on awafer substrate for the production of a microprocessor, comprising: (a)providing a chemically amplified positive tone photoresist, thephotoresist comprising a resin, a photoacid-generating compound and anamine other than a trialkylamine; (b) forming a layer of a photoresistcomposition on the wafer substrate and exposing the photoresist layer toan image pattern of activating radiation; (c) developing the exposedphotoresist layer to form a photoresist relief image.
 2. The method ofclaim 1 wherein the amine is an aryl-substituted amine.
 3. The method ofclaim 1 wherein the amine is a cyclic amine.
 4. The method of claim 1wherein the photoacid-generating compound is an iodonium compound. 5.The method of claim 1 wherein the photoacid-generating compound is anaromatic sulfonium salt.
 6. The method of claim 1 wherein substrateareas bared of the photoresist layer upon development are selectivelyprocessed.
 7. The method of claim 1 wherein substrate areas bared of thephotoresist upon development are chemically etched.
 8. The method ofclaim 1 wherein substrate areas bared of the photoresist layer upondevelopment are plated.